1. Field of the Invention
The present invention generally relates to a woven fabric which is designed for use in a paper, cellulose or board manufacturing machine, and which along each end, has a plurality of loops to be included in a seam to form an endless woven fabric. The invention also relates to a method of manufacturing such a fabric.
2. Description of the Prior Art
Seamed papermaking fabrics have seams that allow the fabric to be assembled and disassembled on a papermaking machine without the requirement of stitching or weaving. Prior art seamed fabrics can be divided into two basic categories, the first having seams formed outside of the weaving loom and the second having seams formed in the weaving loom.
The first category of fabrics, those having seams formed outside the weaving loom, includes flat woven fabrics with an independent seam structure attached to the ends of the fabric, such as by sewing a woven tape onto the fabric or piercing it with clipper hooks. These structures have provided poor caliper and density profiles in the seam area. Other structures, such as described in U.S. Pat. No. 4,244,084, are formed with an area free of cross direction yarns near each end of the fabric. Loops are formed by folding each end of the fabric back along itself and then stitching each end to hold the folded ends. This structure again provides poor caliper and density profiles in the seam area due to the fold back thickness, and has a strength and life which is limited to the strength of the stitching holding the folded fabric. These problems have effectively precluded the successful use of any of these types of fabric seams in the wet press section of papermaking machines. Seam loops have also been formed on flat woven fabrics by tying back machine direction yarns at each end of the fabric. However, tying back is generally a time consuming process which must be performed after the fabric is woven.
In the second category, in which a pin seam is formed during the weaving process on the loom, a conventional approach for forming such seam loops is shown in U.S. Pat. No. 3,815,645. In that process, pairs of weft yarns are woven around a forming wire to form the loops and then the forming wire is removed. Seam loops formed by this process are often difficult to mesh together because of their inconsistent sizes, shapes and orientations which result from the weaving method. In addition, when the forming wire is removed, the resultant fabric is generally a flat fabric with loop ends at each end thereof. Along the length of the fabric, the warp yarns weave with both layers of weft yarns, thereby joining the two weft yarns together.
Accordingly, there exists a need for a base fabric having seam loops which provide better fabric properties in the seam area while being easier to make and install.